Filter apparatus use in a photographic printer

ABSTRACT

A rotatable disc is provided, for use in a photographic printer, supporting both scanning and large area transmissive filters. The disc is used to selective position a scanning or large area filter between a photographic negative and a single light sensor. The disc thus permits the single light sensor to be used to measure both the scanned and large area transmissive characteristics of the photographic negative.

This application is a continuation of application Ser. No. 357,680,filed 5/26/89, now abandoned, which was a continuation of Ser. No.062,523, filed 6/12/87, now abandoned.

REFERENCE TO RELATED APPLICATIONS

Reference is hereby made to related, copending applications (Title:PHOTOGRAPHIC PRINTER, Inventor: J. Morse; Title: PHOTOGRAPHIC PRINTER.Inventors: E. Goll, J. Carson; Title: PHOTOGRAPHIC PRINTER INCLUDINGINTEGRAL REFLECTION DENSITOMETRY APPARATUS, Inventors: E. Goll, D.Beaulieu) filed concurrently herewith.

BACKGROUND OF THE INVENTION

The present invention relates generally to photographic printers andmore specifically to a filter apparatus for use in a photographicprinter which permits the selective positioning of a scanning or largearea transmissive filter between a negative and a single light sensor.

In the process of developing photographic negatives, printing thenegatives, and developing the prints, it is necessary to measure variousdensity characteristics of both negatives and prints. For example, tomonitor the quality of a film processor, it is necessary to measure thetransmissive characteristics of a developed strip of transmissive testpatches, commonly referred to as a film process control strip. Toproperly control exposure when printing negatives, it is common practiceto scan the transmissive characteristics of each negative at a pluralityof discrete locations whereby to measure the scanned transmissivedensity of each negative. To monitor the quality of a paper processor,it is necessary to measure the reflective density of a developed stripof reflective patches, commonly referred to as a paper process controlstrip.

Making these various types of densitometric measurements requires theuse of different filters. More specifically, measuring the scanneddensity of a transmissive pictorial negative typically requires thescanning of many small, transmissive scanning filters between thenegative and a light sensor. Scanning a pictorial color negative mayrequire, for example, twelve (12) each of red, green, and blue scanningfilter. Measuring the large area reflective or transmissive densities ofreflective or transmissive color patches requires at least one each red,green, and blue large area transmissive filters.

It is known in the art to provide photographic printers includingrotatable discs supporting the required plurality of scanning filters ofnecessary color (i.e. passband). These discs are rotated between thenegative and a light sensor to measure the transmissive characteristicsof the negative. These transmissive characteristics are subsequentlyused to calculate the scanned densities at a plurality of discreteregions on the negative. Such discs, however, make no provisions for thelarge area transmissive filters required to measure large areatransmissive densities.

U.S. Pat. No. 3,229,574 to Neale et al. shows a filter wheel includingred, green, and blue large area transmissive filters. The wheel iscontrolled so as to selectively position each of the filters between thenegative and a light sensor, whereby to measure the large areatransmissive characteristics of the negatives. These large areatransmissive characteristics are subsequently used to calculate thelarge area transmissive densities of the negatives. Neale et al.,however, makes no provisions for measuring the scanned density of thenegative.

In the prior art it is thus necessary to provide substantially separatefilter positioning and control apparatus for measuring scanned and largearea characteristics of negatives or test patches. Further, because suchapparatus is separate, two or more photocells are often required, onebeing associated with the apparatus for measuring the scannedtransmissive characteristics, and one being associated with theapparatus used to measure the large area characteristics.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide in aphotographic printer apparatus for controlling and positioning filterswhich permits the measuring of both scanned and large areacharacteristics of negatives and test patches, is straight-forward andeconomical in construction, and requires a minimum of parts.

Another object of the present invention is to provide a single rotatabledisc supporting both scanning and large area filters, such disc beingadapted for use in a photographic printer to measure both scanned andlarge area characteristics of negatives and test patches.

SUMMARY OF THE INVENTION

Filter positioning and control apparatus is provided for use in aphotographic printer including means for holding a photographic negativeand a single light sensor. In accordance with the invention, means areprovided for selectively positioning a scanning transmissive filter or alarge area transmissive filter between the photographic sensor and thelight sensor.

In a preferred embodiment of the invention, the means for selectivelypositioning the scanning or large area transmissive filters includes arotatable disc supporting at least one each red, green and blue scanningtransmissive filters, and one each red, green, and blue large areatransmissive filters.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention, together with further objects thereof, will be betterunderstood from a consideration of the following description inconjunction with the drawing figures, in which like reference numeralsare carried forward, and in which:

FIG. 1 shows a schematic view of a color photographic printerconstructed in accordance with the present invention;

FIG. 2 shows a front view of the scanning disc of FIG. 1;

FIG. 2A shows a schematic view of the position sensing mechanism of FIG.1;

FIG. 3 shows a schematic diagram of AMP/CONVERTER 25 of FIG. 1;

FIG. 4 shows a top view, partially in schematic, of a portion of FIG. 1including details of the reflection densitometry apparatus of FIG. 1;

FIG. 5 shows a perspective view of the carrier of FIG. 4;

FIG. 6 shows a back view, partially in schematic of the reflectiondensitometry apparatus of FIG. 4;

FIG. 7 shows an alternate embodiment of position sensing mechanism 116of FIG. 6; and

FIG. 8 is a sectional view of FIG. 7 taken along line 8--8.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a color photographic printer 20 includes alight source 22 and photodiode 24, both situated on a common opticalaxis 26. Light source 22 is directed so as to project light along axis26 towards photodiode 24. Light source 22 comprises, for example, atungstenhalogen lamp 22A incorporating a "cold-mirror" reflector 22B,and also a heat absorbing glass plate 23. photodiode 24 comprises, forexample, a blue-enhanced silicon diode. An amplifier/converter unit 25(described in detail below) is connected to the output of photodiode 24,the two forming a photometer 27.

Adjacent light source 22 are three subtractive light filters, a Cyanfilter 28A, a Magenta filter 28B, and a Yellow filter 28C. A coloredbalance filter, in this embodiment of the invention a red-yellow balancefilter 28D, is disposed between Cyan filter 28A and light source 22.Each filter 28A-28D is connected to a filter control mechanism 30, thefilter control mechanism comprising a separate rotary solenoid connectedto each filter. The rotary solenoids are indicated at 30A-30D incorrespondence with the filters 28A-28D. Filter control mechanism 30operates to selectively dispose filters 28A-28C into the light pathalong axis 26 to stop exposure of their respective colors. Filtercontrol mechanism 30 further operates, in a manner described in furtherdetail hereinbelow, to selectively dispose filter 28D out of the lightpath along axis 26 when scanning a negative, and into the light pathwhen exposing/printing a negative.

Adjacent filter 28C and centered on axis 26 is a light integrating box(LIB) 32. LIB 32 comprises, for example, a reflecting box 32A having alight-reflecting interior, including pyramid glass 32B at a first endproximate light source 22, and a diffuser 32C at the opposing secondend. Situated adjacent LIB 32 between light source 22 and photodiode 24is a film negative 34 to be printed. Negative 34 typically comprises oneof a roll or disk of negatives, such as 135 or 110 type photographicnegatives, and is supported in an appropriate holder and advancemechanism 35. As used herein, the term "negative" includes alltransparent film images, including photographic transparencies.

Situated between film negative 34 and photodiode 24, in a plane of focusperpendicular to and substantially centered on axis 26, is an opticallytransparent paper platen 36 comprised, for example, of an opticallyclear glass. A projection lens 38 and dark shutter 40 are disposed,respectively, between negative 34 and paper platen 36. Disposed adjacentplaten 36, between the platen and photodiode 24, is a field lens 42.Field lens 42 preferably comprises a fresnel lens, chosen for itssubstantially flat, thin dimensions. Adjacent field lens 42, between thefield lens and photodiode 24, is a reflection densitometry assembly 50(described in detail below). Situated between reflection densitometryassembly 50 and photodiode 24 are, respectively, a relay lens 44, arotating scanning disc 46, and a condensing lens 48. A position sensingmechanism 51 is positioned adjacent the edge of scanning disc 46.

Disposed proximate one end of platen 36 is a roll-paper dispensingmechanism 52 containing a roll 54 of unexposed photographic paper.Proximate an outlet 52A of roll-paper dispensing mechanism 52 is acutting mechanism 56, such as a blade. In FIG. 1, printer 20 is shownwith a portion 58 of unexposed photographic paper 54 dispensed fromroll-paper dispensing mechanism 52 so as to overlay platen 36 with thelight-sensitive side facing negative 34.

It will be understood that the various lenses including projection lens38, field lens 42, relay lens 44, and condensing lens 48 comprise lensesof standard design selected to provide appropriate focal lengths andf-stops (apertures).

A digital computer 60 is provided for controlling printer 20 and forinteracting with a 25 human user (not shown) via a keyboard and displayunit 62. Computer 60 is connected to photometer 27 viaamplifier/converter unit 25. Computer 60 is further connected to filtercontroller 30, roll-paper dispensing mechanism 52, reflectiondensitometer apparatus 50, film holder and advance mechanism 35, darkshutter 40, position sensing mechanism 51, and a paper processor 64.

Referring now to FIG. 2, scanning disc 46 comprises an improvement towhat is typically referred to in the art as a Nipkow disc. In accordancewith the known features of a Nipkow disc, scanning disc 46 includesthree spirally disposed rows of scanning filters including a set of Redscanning filters 66, a set of Blue scanning filters 68, and a set ofGreen scanning filters 70. Each set of filters 66, 68, 70 includes tensmall apertures 72, each aperture being overlaid with an appropriatelycolored filter. Filters 66, 68, 70 each preferably comprises abroad-band filter so as to provide adequate light to photodiode 24 whenmeasuring scanned densities as described in detail below. Further inaccordance with the known features of a Nipkow disc, scanning disc 46includes a plurality of timing marks 74 and a single starting mark 75disposed about its periphery. In a manner described in detail below,timing marks 74 and starting mark 75 are used to determine the relativeposition of the various apertures on scanning disc 46 with respect tooptical axis 26, and to communicate this information to computer 60 viaposition sensing mechanism 51.

In accordance with the improvements of the present invention, scanningdisc 46 further includes Red, Green, and Blue large area transmissive(LAT) filters, indicated at 76, 78 and 80, respectively. Each LAT filter76, 78, 80 comprises an aperture relatively larger than aperture 72overlain by an appropriately colored filter. LAT filters 76, 78, 80 eachpreferably comprises a narrow-band filter for providing the desiredprecision when performing LATD measurements as will be described indetail below. LAT filters 76, 78 and 80 are positioned relative totiming marks 74 and position mark 75 so that their position relative toaxis 26 can be determined by computer 60.

Referring now to FIG. 2A, position sensing mechanism 51 comprises a pairof light-emitting diodes (LED's) 83, 85, situated on a first side ofscanning disc 46 and positioned to project light through timing marks 74and starting mark 75 of the scanning disc, respectively. Positioned onthe opposite side of scanning disc 46 are a pair of photodiodes 87, 89.Photodiodes 87, 89 are located so as to oppose LED's 83, 85,respectively. Hence, photodiodes 87, 89 sense the position of scanningdisc 46 by monitoring the rotation of timing marks 74 and starting mark75, respectively.

Referring now to FIG. 3, an exemplary embodiment of amplifier/converterunit 25 is shown for converting a current I_(pd) output by photodiode 24to a digital output code D_(O-N) for processing by computer 60. It willbe understood that the exact structure of photometer 64 does notconstitute a portion of the present invention, and thus theimplementation of such circuits is not treated exhaustively herein.Amplifier/converter unit 25 includes a high gain current-to-voltageconverter 130 connected to a temperature compensated, precision currentsource 132. The output of current source 132 is connected to alogarithmic amplifier (log amp) 134, the current source and log amp bothbeing supplied with a reference voltage V_(refl) by a reference voltagegenerator 136. The output of log amp 134 is connected to a 10-bit A/Dconverter 138. the A/D converter being supplied a reference voltageV_(ref2) by a second reference voltage generator 140. The 10-bit digitalword output D_(O-N) of A/D converter 138 is connected to computer 60.

In operation, picoamp-level current I_(pd) is converted to an amplifiedvoltage V₁, which is in turn converted to a nanoamp-level current I₁ bycurrent source 132. Current I₁ is converted to an amplified log voltageV₂ by log amp 134. Log voltage V₂ is subsequently converted to a 10 bitdigital word D_(0-N) by A/D converter 138, which is read and stored bycomputer 60 as described below. Reference voltage generators 136 and 138are used to calibrate current source 132, log amp 134, and A/D converter140. Photometer 27 exhibits an operating range of approximately threedecades.

In accordance with the present invention, printer 20 operates in threebasic modes to provide the capabilities of: (1) measuring the LATDand/or scanned densities of negatives, and printing those negativesaccording to their measured transmission characteristics; (2) measuringthe LATD of transmissive test patches; and (3) measuring the large areareflective density (LARD) of reflective test patches. All measurementsand printing are performed on optical axis 26 using single photodiode24. For purposes of explanation, these modes of operation will bedescribed separately below.

In the preferred embodiment of the invention, the first mode ofoperation described immediately above is performed using the scanneddensities of the negatives, and will thus be referred to herein as the`scan and print` mode of operation. In the scan and print mode ofoperation, negative 34 is loaded into holder and advance mechanism 35.With no paper on platen 36, and with filters 28A, 28B, 28C, and 28D allremoved from the light path along optical axis 26, light source 22projects light along axis 26 towards photodiode 24. This projectedlight, illustrated by dashed-line rays 84, is diffused by LIB 32 so asto impinge uniformly on negative 34. Dark shutter 40 is opened to passlight, and the light projected through negative 34 is focused byprojection lens 38 onto glass platen 36. Because no paper is on platen36, the light passes through the platen and is focused by field lens 42onto relay lens 44. In this scan and print mode of operation, reflectiondensitometer apparatus 50 is transparent to this projected light.Scanning disc 46 is rotated by a motor (not shown). Relay lens 44focuses the projected light through a medial region of scanning disc 46towards condensing lens 48. Relay lens 44 and scan disc 46 are alignedsuch that all of the filters on the scan disc pass through the lightoutput of the relay lens. As scan disc 46 rotates, each of scanningfilters 66, 68, 70 will scan substantially the entirety of theprojection of negative 34, while large area transmission filters 76, 78,80 each will intercept substantially the entirety of the projection. Theportions of the light filtered by the various filters on scanning disc46 are subsequently focused by condensing lens 48 onto photodiode 24.

As a first step in the process of scanning and printing negative 34,computer 60 controls the scanning of the negative by R, G, and Bscanning filters 66, 68 and 70, respectively, on scanning disc 46. Thisscanning is performed by storing the output of photometer 27 in computer60 as the various apertures 72 in the scanning filters 66, 68, 70 passpreselected regions of the light projected through negative 34. Computer60 controls the scanning by monitoring the position of timing marks 74and starting mark 75 using position sensing mechanism 51. The locationof the various filters on scanning disc 46 being known relative totiming marks 74 and starting mark 75, computer 60 uses this informationto calculate when a selected window 72 of a scanning filter 66, 68, 70is aligned with a selected region of negative 34. Computer 60 thenstores the output of photometer 27 at the calculated time. It will beappreciated that in this manner substantially the entirety of negative34 can be scanned in as many discrete units as is desired, the onlylimitation being the physical limitations of the equipment. The scannedtransmissive densities of negative 34 thus obtained are stored in amemory (not shown) of computer 60 for subsequent use in determiningexposure times for the negative.

At this point in the process of printing negative 34, computer 60 hasscanned and stored the transmissive density of the negative at aplurality of locations. For example, and without limitation, it may bedesired to utilize scanning disc 46 in the manner described above toscan 80 discrete units of negative 34 to determine the R, G, and Bdensity of each of these units. Using these scanned transmissive densitymeasurements, computer 60 now calculates an appropriate exposure timefor printing negative 34 onto the portion 58 of unexposed photographicpaper 54 which will be advanced to overlay platen 36 in the mannerdescribed below. It will be understood that one of many known algorithmscan be utilized to calculate the printing exposure time. Such algorithmscan include, for example, the use of a printing density conversionmatrix in computer 60 as a first step in calculating exposure times in amanner well known to those skilled in the art. The selection of anappropriate algorithm is not a part of the present invention, and willnot be discussed in detail herein.

Subsequent to the conclusion of the scanning step, and after theinitiation of the exposure calculations, dark shutter 40 is closed. Thelight projected by light source 22 is stopped by dark shutter 40, androll-paper dispensing mechanism 52 is actuated by computer 60 to unrollunexposed paper portion 58 onto platen 36.

With the light-sensitive side of paper portion 58 directed at negative34, solenoid 30D of filter control mechanism 30 is used to positionred-yellow balancing filter 28D on axis 26, and then dark shutter 40 isopened to pass light. Cyan, magenta, and yellow filters 28A, 28B, 28C,are manipulated by corresponding 30A-30C of controller 30 to exposenegative 34 onto paper portion 58 in accordance with the results of theexposure algorithm calculation done by computer 60. Upon proper exposureof paper portion 58, dark 20 shutter 40 is closed. Cutting mechanism 56is then activated to separate now exposed paper portion 58 from roll 54,and the paper portion is subsequently removed for development by paperprocessor 64 (the details of which are not shown herein). Filters28A-28D are reset off of optical axis 26 out of the light path. The scanand print process described above is then repeated for subsequentnegatives 34.

In the second mode of operation described above, i.e. measuring the LATDof negative 34 (or a transmissive test patch substituted therefore) thenegative is placed in holder and advance mechanism 35, and paper portion58 is removed from (or not advanced onto) platen 36. Computer 60 thenreads and stores the output of photometer 27 as LAT filters 76, 78 and80 are respectively disposed in the light path along axis 26. In amanner similar to the scanning operation described above, computer 60controls these measurements by monitoring timing marks 74 and startingmark 75 via position sensing mechanism 51. The measured R, G and BLATD's of negative 34 are stored in the memory of computer 60.

It is to be understood that, in the preferred embodiment of theinvention, LATD's are only used to measure the transmissive density oftransmissive test patches, for example to control a film processor (notshown). Scanned transmissive densities are used, in the manner describedabove, to calculate exposure times for pictorial negatives. However,LATD's can be used to calculate the exposure times for pictorialnegatives. Similarly, some combination of LATD's and scanned densitiescan be also used to calculate the exposure times for pictorialnegatives, the densities used being dependent on the types of negativesbeing printed and the exposure calculation algorithm implemented incomputer 60. The scope of the present invention is thus intended tocover all of these density measurement/exposure calculationcombinations.

Referring now to FIGS. 4 and 5, a portion of printer 20 is shownincluding details of reflection densitometer apparatus 50. Apparatus 50includes a removable carrier 90 (best shown in FIG. 5) for supporting apaper strip 92. Carrier 90 comprises two generally rectangular halves90A, 90B hinged along a lower, length-wise edge by hinges 94 so thatthey can be opened to accept strip 92. Four rectangular apertures 96A,96B, 96C, and 96D are disposed in side 90B of carrier 90, theseapertures being generally rectangular in shape and in vertical alignmentwithin the carrier side.

For purposes of explanation, paper strip 92 will be described herein asa paper process control strip including four developed, reflectivepatches 98A, 98B, 98C, and 98D. Patches 98A-98D vary in density fromwhite patch 98D to black patch 98A, each of the patches having a knownexposure. Patches 98A-D are located on test strip 92 so as to be inrespective alignment with apertures 96A-D of carrier 90. Carrier 90further includes a white calibration patch 100 of constant density,disposed permanently on the outer surface of side 90B thereof invertical alignment with apertures 96A-D. Five V-shaped detents areprovided along the unhinged, lengthwise edge of carrier 90, thesedetents being indicated at 102A, 102B, 102C, 102D, and 102E. Detents102A-102D are in vertical alignment with apertures 96A-D, respectively.Detent 102E is in vertical alignment with calibration patch 100. Anupper corner 103 of carrier 90 is chamfered to engage a roller in amanner described in detail below.

Referring back to FIG. 4, it is seen that carrier 90 is supported inprinter 10 so as to be disposed in a plane perpendicular to axis 26.Carrier apertures 96A-D, and hence strip patches 98A-D and calibrationpatch 100, face photodiode 24. A generally U-shaped bracket 104,including a pair of legs 104A, 104B connected by a common base 104C, isdisposed between carrier 90 and photodiode 24. Bracket 104 is disposedsymmetrically about axis 26, with legs 104A and 104B disposed onopposite sides of the axis and projecting towards carrier 90. Each leg104A and 104B supports a lamp 106 in a reflective tube 108. Optionallyincluded in each reflective tube 108 is a heat absorbing glass 109including infrared-rejecting interference filters. Each reflective tube108 functions as an integrating box to direct the light output of thelamp. Each lamp 106 and tube 108 are directed to project light,indicated by rays 110, at the aperture of carrier 90 centered on axis26; i.e. aperture 96C as shown in FIG. 4.

Continuing to describe apparatus 50 as shown in FIG. 4, a movablesupplementary lens 112 is shown situated in base 104C of bracket 104. Alens control mechanism 114, details of which are described below withrespect to FIG. 6, is connected to lens 112 and further connected so asto sense the presence of carrier 90 in printer 20. A position sensingmechanism 116, the details of which are also described with respect toFIG. 6 below, is disposed so as to sense detents 102A-E of carrier 90 asthe carrier is inserted into printer 20.

Referring now to FIG. 6, printer 20 includes a slot 118 for acceptingcarrier 90 and supporting the carrier in the plane perpendicular to axis26. Position sensing mechanism 116 is seen to comprise a spring portion120 shaped and positioned

to engage each respective detent 102A-E, one at a time, as carrier 90 isinserted into printer 20. Spring portion 120 is connected to a pressuresensitive switch 122 which electronically senses the movement of thespring portion through detents 102A-E and transmits this information tocomputer 60.

Lens control mechanism 114 includes a holder 124 for lens 112, theholder being connected to a roller 126 via a pivoting member 128. Aspring 130 normally biases pivoting member 128 in a counter-clockwisedirection about a pivot point 131. With member 128 thus biased, holder124 is normally biased towards the top (as viewed in FIG. 6) of bracketbase 104C such that lens 112 is removed from the optical path along axis26. When carrier 90 is inserted into slot 118, roller 126 engageschamfered corner 103 of the carrier, and pivoting member 128 pivots,thereby sliding lens 112 into a centered position in the optical pathalong axis 26. In FIG. 6, reflection densitometry apparatus 50 is shownin solid line with carrier 90 inserted in printer 20 such that patch 100and lens 112 are both centered on optical axis 26. Further shown, indashed-line, is the engagement of roller 126 with chamfered corner 103of carrier 90.

As described above, in the scan-and-print and LATD measurement modes ofoperation, carrier 90 is removed from printer 20, lens 112 isautomatically removed from the optical path along axis 26, lamps 106 areoff, and reflection densitometry apparatus 50 is effectively transparentto the printer. When it is desired to measure the

large area reflective density of patches 96A-D of paper strip 92, thepaper strip is inserted in carrier 90, and the carrier is inserted inslot 118 of printer 20. Position sensing mechanism 116 senses theinsertion of carrier 90 into printer 20 and signals computer 60. Underthe control of computer 60, lamps 106 are switched on. Roller 126engages carrier 90 and pivoting member 128 pivots to position lens 112on axis 26.

As position sensor 116 senses each respective detent 102A-E, computer 60controls the measurement of the large area reflective density of thecorresponding paper strip patch 96A-D or the calibration patch 100aligned along axis 26. For purposes of explanation, the operation ofprinter 20 in the large area reflection densitometry mode of operationwill now be described with respect to FIG. 4, wherein detent 102C isaligned with axis 26 and paper strip patch 96C is centered about theaxis. Light rays 110 projected by lamps 106 are directed by reflectivetubes 108 through aperture 96C onto paper strip patch 98C, and reflectedtherefrom into lens 112. Supplementary lens 112 forms a virtual image ofpaper strip patch 96C in the plane of fresnel lens 42 for relay lens 44,which in turn focuses this image onto rotating scanning disc 46 in themanner described above. The apertures in disc 46 for the filters 76, 78,80 act as optical field stops to reduce stray light from reachingphotodiode 24 so that only light reflected from patch 92C is measured.The light projected through filters 76, 78, 80 on scanning disc 46 isfocused by condensing lens 48 onto photodiode 24. Computer 60 thenmeasures the light detected by photodiode 24 when LAT filters 76, 78,and 80 (FIG. 2) are aligned, respectively, on axis 26. It will thus beappreciated that LAT filters 76, 78, 80 are used to measure the LATD ofnegative 34 (as described above), or the large area reflective densityof the reflective test patches 96A-D on paper strip 92. The timing ofthis process is controlled by computer 60, using position sensingmechanism 51 in the manner described above.

Thus, as carrier 90 is inserted into printer 20 from left to right asviewed in FIG. 6), reflection densitometry apparatus 50 of the printeris used to measure the large area reflective density of whiteCalibration patch 100, and paper strip patches 96D, 96C, 96B, and 96A,in that order. When the large area reflective densitometry measurementsare complete, carrier 90 is removed from printer 20, and, under thecontrol of computer 60, reflection densitometry apparatus 50 becomesessentially invisible to the printer. If, for example, paper strip 92comprises a paper process control strip, the large area reflectivedensities measured during the above-described reflection densitometrymode of operation would then be compared to previously measured largearea reflection reference densities and limits stored in computer 60.The invention is not thus limited, however, and the reflectiondensitometry capability provided by printer 20 can be used, for example,to measure the LATD of printer control test prints, or to make any otherappropriate reflection densitometry measurements.

FIGS. 7 and 8 show an alternate embodiment of position sensing mechanism116' wherein a pair of LED's 134, 136 and opposing photosensors 138,140, respectively, are used to sense position holes 142 in carrier 90'.LED's 134, 136, and photosensors 138, 140, are fixed on printer 20 onopposite sides of slot 118 (FIG. 6) A separate position hole 142 ispositioned on carrier 90' in fixed relation to patch 100 and eachaperture 96A-96D. Detents 102A-102E are still used to position carrier90' in printer 20. However, computer 60 senses the position of carrier90' by monitoring photosensors 138, 140. Specifically, when carrier 90'is inserted into printer 20, the carrier will block the light pathbetween LED 136 and photosensor 140, turning the photosensor off. Ascarrier 90' is advanced into printer 20, LED 134 and photosensor 138will together sense each hole 142 as patch 100 and apertures 96A-96E arepositioned, sequentially, to perform large area reflection densitometrymeasurements in the manner described above.

There is thus provided apparatus for positioning and controlling filtersin a photographic printer which permits the selective positioning ofeither a large area or scanning transmissive filter between aphotographic negative and a single light sensor. In a preferredembodiment, the apparatus includes a single rotatable disc supporting aplurality of red, green, and blue scanning transmissive filters, and oneeach red, green, and blue large area transmissive filters. A sensor andcomputer are provided for determining the relative position between thefilters, negative, and light sensor, such that once the desireddensitometry measurements are selected by the operator, the positioningof the filters is substantially automatic.

While a preferred embodiment of the invention has been illustrated anddescribed, it will be clear that the invention is not so limited.Numerous modifications, changes, variations, substitutions andequivalents will occur to those skilled in the are without departingfrom the spirit and scope of the present invention.

What is claimed is:
 1. In a photographic printer, apparatuscomprising:means for holding a photographic negative; a single lightsensor; a rotatable disc having a disc center and being disposed betweensaid photographic negative and said light sensor; said rotatable dischaving first, second and third angularly=displaced, equal sizedapertures located at the same radial distance from said center andrespectively supporting red, green, and blue large area transmissivefilters; said rotatable disc further having first, second and thirdangularly-displaced, spirally disposed rows of a like number of equalsized apertures, the apertures in each row being located at differentradial distances from said center with the corresponding apertures ofdifferent rows being located at the same radial distance from saidcenter, and respectively supporting red, green, and blue scanningfilters over said rows of apertures; the apertures over which saidtransmissive filters are supported being relatively larger than theapertures of said rows over which said scanning filters are supported;means including at least one optical lens disposed intermediate saidrotatable disc and said light sensor for focusing light projectedthrough said photographic negative and any selected one of the aperturesof said large area transmissive or scanning filters onto said lightsensor; and means for determining the position of the filters on saidrotatable disc relative to said photographic negative and said lightsensor.
 2. The apparatus of claim 1 wherein:said photographic negativeis disposed in a plane generally perpendicular to and centered on anoptical axis; said light sensor is disposed generally on said opticalaxis; and said rotatable disc is disposed in a plane generallyperpendicular to said optical axis.
 3. The apparatus of claim 2 andfurther including means for rotating said rotatable disc; and whereinsaid position determining means comprises:said disc further including aplurality of indices disposed about the periphery thereof; meansdisposed proximate said rotatable disc for sensing said indices as saiddisc is rotated; and means connected to said sensing means fordetermining the position of said scanning and large area filtersrelative to said light sensor as said rotatable disc rotates.
 4. In ascanning filter disc of the Nipkow type, having a rotatable discsupporting three spirally disposed rows of scanning filters including aset of red scanning filters, a set of blue scanning filters and a set ofgreen scanning filters, each set of filters including a plurality ofapertures overlain by an appropriately colored filter, and the discincluding a plurality of timing marks and a starting mark disposed aboutthe periphery of said disc and used to determine the relative positionsof the various apertures on the scanning disc with respect to an opticalaxis, the improvement comprising said scanning disc further supportingred, blue and green large area transmissive filters, each including anaperture relatively larger than said scanning filter apertures andoverlain by an appropriately colored filter, the large area transmissivefilters being positioned relative to said timing marks and starting markso that their positions relative to said optical axis can be determined.5. The apparatus of claim 1, wherein at least one of said large areatransmissive filters is of a different bandwidth than the correspondinglike-colored scanning filter.
 6. The apparatus of claim 1, wherein saidlarge area transmissive filters are of different bandwidths than thecorresponding like-colored scanning filters.
 7. The improvement of claim4, wherein at least one of said large area transmissive filters has abandwidth narrower than the corresponding like-colored scanning filter.8. The improvement of claim 4, wherein said large area transmissivefilters are of narrower bandwidths than the corresponding like-coloredscanning filters.